23cm on two Watts and a prayer

A few month back one of the members of my radio club posted to the clubs group.io group that he had participated in the April 23cm UKAC using a his new IC9700 and a tri-band vertical and managed three OSO's.    

His foray into the world of 23cm's had me dusting off my SG-Labs 23cm transverter I had bought a few years previous and had sat on the shelf and actually give it a whirl. 

The transverter is the MKII version and has a power output of 2.5W so real QRP compared to the IC9700's 10W.  The only antenna I had was a similar tri-band (Comet GP-95N) with a gain of 12.8dBi if you believe that?  The feeder was 15m of Ecoflex 10 so feed losses were going to be around 2.47dB.   So all things considered ERP would be around 16.5W.    

Using an FT817 with the above setup I entered my first 23cm UKAC and was amazed to work 7 stations with the best DX being G3MEH at 105km.  

I can't remember now if I used the ON4KST microwave chat during the first contest but I believe I didn't but with all subsequent contests I did.  

Anyway I was actually amazed I did so well with such low power and polarisation mismatch but that one contest had given me the incentive to do the next contest.

For the June contest I made the easiest change I could and bought an 18 element Yagi a  PA1296-18-1.5RB from Antenna Amplifier in Serbia.  The antenna gives a reported gain of 17.16dBi this of course gave me an increase in ERP from 16.5W to 45W which should give me improvement of around half an S-point and of course the 30dB improvement from having no polarisation mismatch. 

You can see from the table below there has been a steady improvement in points and DX though in August there was some great tropo as shown by the fact I worked OZ1FF on 2W though it was mainly sea path but neither the less I was extremely happy.

Month	QSO's	Points	DX Km
May	7	1877	105
June	11	2154	105
July	11	3070	180
August	11	3624	208
September	19	8357	670

So the next easy upgrade will be replacing the current feed cable with Ultraflex 13 but that will only yield another dB but it will be in place for the October contest.   

Next up will be finishing off the 80W amplifier I'm building and sticking it in a box.     The finished unit will have a LPF by John G3XDY, a 80W PA based up John G4BAO well known design with a homebrew controller to switch the pa and tvrx while also displaying output power, temp and VSWR. 

QO-100 VFO display for Elecraft K3s and Yaesu FT817

I've been using SDR-Console to listen to QO100 and now I've almost completed my uplink equipment I want some way of seeing what the uplink frequency should be when tuned to a particular downlink one so I knocked up a quick Python script to show me what the uplink and downlink frequency would be when tuning my Elecraft K3s or FT817.

To use it you'll need Python 3 with PyQt5 and PySerial installed.   

Edit the config.ini and set the LO in Hertz which in my case was my 70cm so 432000000

Example:

[CONFIG] LO = 432000000 PORT = COM10 BAUD = 38400 POLL = 0.01 RIG = K3S

To start the application from the command line do. 

python QO100uplinkVFO.py

If that'll be useful you can download the software from GitHub.

   

Dual Transverter IF switch and Sequencers for Elecraft K3 / K3s

I have a medical condition called Muscular Dystrophy which results in the muscles of body slowly atrophying over time which has resulted in my hand muscles weakening to the point I struggle connecting and disconnecting any type of RF connector; this poses a problem in that I use transverters for my 2m and 70cm systems and constantly need to swap the 28MHz IF lines.

A sequencer is also employed to ensure any pre-amps are switched out of the TX signal path as well as to ensure hot switching doesn’t occur to any relays when RF is generated by the exciter.

My original setup used a single sequencer shared between transverters and other devices and though this was perfectly adequate I wanted the new system to have separate sequences where each event could be configured or modified at a later date without too much hassle.

Original Setup

Both of the transverters were built with a single RF port with an internal relay however this isn’t ideal and so I decided to modify both my transverters to provide a separate RX and TX RF ports.

My station also utilises a Wavenode RF power meter to monitor in real-time the VSWR of each antenna.  In the event of a high VSWR the Wavenode closes an internal relay this can be used to connect to an external monitor to cease operation of the station.

I recently purchased an Elecraft K3S (K3) which provides both RX and TX IF ports with the TX port output at 0dBm giving the correct level of drive for the transverters.

While reading the K3 manual I discovered the ACC port provides four TTL level logic gates where a combination of the four indicates which band is currently selected.

So with the above in mind, I decided to completely re-engineer the station to give the best receive and transmit performance I could get on the 2m and 70cm bands, reduce the amount of cable swapping and have separate sequencers for each of the transverters

The ACC port can provide PTT and TX inhibit functions which again would also reduce the amount of cabling required.

The ACC port consists of a DE-15 socket where pins 3, 9, 13 and 14 provide access to the TTL logic gates and pins 7 and 10 provide the TX inhibit (TXINHIB), which can be configured to inhibit the exciter on either a high or low state and KEYOUT-LP (PTT) which provides a 10mA sink to ground.

This was exactly what I needed to create a single control unit to switch IF lines, provide an independent sequencer to each transverter chain and to ensure that no RF was generated until all events in each sequence was completed all at the press of the band selector button on the K3 after some thought I came up with the following station configuration.

New Setup

The K3s band logic gates can be configured in one of three ways NOR for HF bands only, TRN for transverters only and HF-TRN for both the HF bands and transverters. I selected the TRN setting which made reading the TTL logic simpler as it only requires knowing the current state of two of the logic gates instead of the four gates required for the NOR or HF-TRN configurations.

From here on forward when I reference bands it is taken to also include the transverters.

The band switch logic matrix for the K3 is shown below.

K3 band switch matrix

As you can see from the table when TRN1 or TRN2 is selected the logic can either be on or off for either band but they can neither be off or on together for band 0 and 1 so any other state would be equal to another band.

So with the above in mind, I needed firstly someway to read the K3 TTL logic.

Secondly, to key the 2m and 70cm transverters as well as associated amplifiers a 10mA sink to ground is needed.

Thirdly the change over relays, Tohtsu CZX-3500, which require 12V and draw around 250mA, which would be held closed for RX operation and released for TX. The CZX-3500’s also have an advantage or providing an extra 20dB of isolation between ports compared to the ones in the transverters which only provided 40dB of isolation.

Fourthly the ability to control two mini relays to switch the IF lines between transverters.

It would also be useful to have some indication of which band has been selected as a separate confirmation to the K3, and that events for that band are being sequenced correctly.

And finally, it would be nice to have some kind of audible alert in the event of a high VSWR.

I came to the conclusion using an Arduino microcontroller would be the easiest route to getting something working fairly quickly with little expense as well as keeping the electronics side of things simple.

The Arduino UNO uses an ATMega328P which has 23 general-purpose digital I/O pins available however two are used for serial coms and one for a reset button, two pins are used for an external 16MHz crystal reference, so minus those five I/O pins eighteen pins are available to for other purposes.

I decided I need the following pins:

2 pins to read the band switch TTL logic from the K3.
3 pins to light LED’s to indicate which band has been selected on the unit.
2 pins for the IF relays.
1 pin to monitor PTT enabled from the K3.
1 pin for a PTT LED indicator.
1 pin to enable and disable TX Inhibit function on the K3.
1 pin to monitor the VSWR trip alert from the Wavenode RF power meter.
1 pin for the VSWR trip enabled warning buzzer.
1 pin for a VSWR trip reset button, for which I’ll use the default Arduino reset pin.
6 pins for the two sets of three for the sequencer, one set for each band selected.

Programming the Arduino is fairly straight forwarding using the Arduino IDE from the Arduino website. The language used is a subset of the C/C++ language which is fairly simple to use and there are plenty of resources on the internet to get you started.

The first iteration of the software was a simple loop that read the state of the I/O pins that monitor the band logic gates on the K3 and lit an LED to indicate which transverter / band was selected.

What became apparent with this first simple loop was despite the fact there aren’t any mechanical switches the software was experiencing contact bounce.

Contact bounce is caused when a switch is pressed or released and for a few milliseconds or more the switch state is unstable to get around this problem it is normal to get the state of the I/O pin and store it in variable and then wait for a defined period and check again when the stored state and current state are equal we can be sure the switch is either high or low.

There were two issues caused by the contact bounce, one if the Arduino was switched on before the K3 then the band selected on the Arduino may not agree with the band selected on the K3 and secondly, when the band was changed on the K3 occasionally the wrong band was detected.

To resolve for these issues I started writing a routine to take into account the unstable state of the switch while bouncing but in a sudden moment of genius decided not to reinvent the wheel and instead download and installed a library called Bounce2.h which reduced the amount of code I had to write for myself.

With the contact bounce cured it took an evening to write the software and that included having to remind myself how hardware is referenced on the Arduino, the web is great for these kinds of projects there’s always plenty of example code around if you’re unsure how to do something.

With the software written the next thing to do was get on with the hardware, now electronics isn’t my forte so this wasn’t something I was looking forward too.

I knew for sequence events two and three some simple NPN transistors in low side configuration would suffice however for event one I needed the ability to switch between 5V to 48V drawing up to 1A so that in the event I need to replace the change over relays I wouldn’t be restricted in what hardware could be used, so I chose to use a P-Channel MOSFET in a high side configuration.

Switch Configurations

I had a discussion with a friend who convinced me that isolating the high voltage side of the circuit would be prudent, it’s not something I would have bothered with however optoisolators are cheap as chips so I decided to isolate all of the sequencer events this would allow me to change the hardware configuration at a later date if I wanted to.

 As I had moved to the optoisolators I decided instead of turning the sequencer event indicator LED’s on direct from the ATMega I/O pins I would instead add an NPN switch in parallel to the optoisolators to sink the LED cathodes to ground instead.

This seems to be overkill but as MMBT3904 NPN transistors are only five pence each including them wasn’t going to cost any significant amount and ensure if I altered the circuit, later on, I wouldn’t run foul of exceeding the 20mA limit on the ATMega I/O pins.

Opto-isolated Switch

The complete circuit diagram is as follows.

The complete schematic

With a general plan of action, I decided instead of building the unit on stripboard I would instead have a go at using KiCad, to develop both the main PCB and front panel LED PCB.

Main board

Front panel

 I decided to place all the LED indicators, high VSWR buzzer and reset button on a small PCB, shown left, which could then be mounted to the front of the case this removed a lot of wiring that would have been required if I had mount everything individually. I used IDC connectors to connect the two boards.

The KiCad project files, Gerber files and software can be downloaded from GitHub.

I do have a couple of sets of boards spare if anyone wants to build one of these units please drop me an email, see QRZ.com, if interested.

Once the PCB’s had arrived and populated I mounted them in a Hammond ‘1550’ 275 x 175 x 67mm die-cast enclosure which matched the transverters.

Font Panel

Rear Panel

Interior

Just a quick update to say I'm still kicking.

Been a quiet month or so and so I thought I better write something for this blog.  ;-)

First off I got fed up trying to get a clean signal from the Gemini 2-500 PA using the Anglian transverter and Icom 7300.   No matter what I seemed to do I could not stop it from occasionally causing splatter, along with the RF surges in power when first keying the transmitter.    Now this isn't to say the IC7300 is a bad radio it isn't but it certainly doesn't like playing the transverter and Gemini.    So to resolve the issue I went and bought an Elecraft K3S which has resolved all the issues and ok it's an expensive fix but the transmitter of the K3S is certainly worlds ahead of the IC7300, though I do still prefer the audio from the 7300 which is much easier on the ears.  

One of the nice things about using the K3S is the fact it displays the right frequency when using the transverters and in fact with in a few days of having it I also discovered it out from TTL logic from the ACC port so you can interface some kind of transverter switching.    

With the above in mind I wondered if a simple transverter switch and device sequencer could be bought and though I did find a couple they were quiet expensive so I decided to roll my own using an Arduino so a couple of prototypes later I've come up with a design with will switch between my 2m and 70cm transverters and handle the device sequencing for both units below is a couple of screenshots from KiCad of the front panel indicator and main board.  I'll do a full write up once I've confirmed all works as expected.  

A quick feature list is as follows.

1. Handles two transverter. 
2. Provides TX inhibit. 
3. First sequence event can provide 12 - 28V up to a couple of amps to drive change over relays.
4. Sequence events two and three can sink up to 40mA, though you could chuck in a darlington pair if you want to sequence more relays.
5. The unit interfaces with my Wavenode so that if a high VSWR is seen the unit automatically ceases transmitting and puts the unit into the default RX mode.
6. All sequence event are optocoupled to the Arduino just in case a FET or BJT decides to go legs up in a funny way.

Front panel layout from KiCad

Main board layout from KiCad.

I've also got another project on the go in the form of a 70cm 250W amplifier which I bought from eBay from a German amateur which was quite cheap at 55 Euros.  

70cm 250W PA module from eBay.

I rather helpfully came across the website of PA0EHG who had bought the same unit and documented what he had done to get the unit going on the 70cm band so once I've got a replacement RF terminator as the one that came with the unit the solder tab fell off as soon as I touched it I'll power it and see what's what.

So that's the end of this update I'll do a proper update once everything has progressed a bit further.

Kuhne Electronics IC7300 IF Transverter Mod Board - Update 2

I original posted I had issues with the Kuhne IC7300 IF interface and had removed the modification, I now believe the issue was partially the interface and board and partially a user issue.

I bought a new interface board and fitted it along with the additional 47ohm resistor that is meant to resolve the TX oscillation issues and so far no funnies have been seen.

The issues I originally reported with the RX side of things were all due to my lack of understanding than to do the interface board.  

The main issue was the Anglian 3L transverter gives about 21dB gain this is such a high amount of gain it reduced the dynamic range considerably which though it made the receiver very hot it also picked up all the local RF noise was causing me a headache.

What I've since realised is I should have added some attenuation to the RX path before the 7300 in fact I've added just enough to give me a noise figure or around 2dB which is in line with the quoted specification for the Anglian this results in almost no loss in dynamic range.

The only problem I found was having such a hot receiver was I need to pay a lot more attention to local generated RF noise than I had previously and after an afternoon of slowly switching all the electronics off the house and a huge amount of ferrite I managed to reduce the noise and birdies by 10dB.

So I need to apologise to Kuhne for writing such a horrid review of the IC7300 IF interface when the reality is most of the issues were down to me being a draft bugger.

Kuhne Electronics IC7300 IF Transverter Mod Board - Update

I recently fitted the Kuhne IF transverter modification board and found I had some issues with it.

When I first fitted the board I had a strange pulse appear on receive when using the transverter I original put this down to having to much signal going from the transverter to the rig and so switched on the rigs attenuator to resolve the issue.   Now I didn't do this in a very scientific manner I just put the attenuation in on gut feeling.

Next I noticed when using my Wavenode power meter when I de-keyed the transmitter I had a 1.3W RF spike out of the transverter which resulted in a 200W spike from the linear.   After pulling the system apart in an effort to resolve the issue I discovered the cause was the Kuhne modification.

As I found the issue with the Wavenode was caused by the interface board I had another look at the RF pulse I was seeing without the rigs attenuator turned on.   I tuned in the GB3VHF beacon which appeared as S9 on the S meter while using the transverter with the combiner and then switch back to IF interface where GB3VHF stayed at S9 without the rigs attenuator turn on however the pulse was present again so I again switched the attenuator back on resulting in the beacon losing an S point but the pulse had disappeared.

I did a quick search on the internet and found on the IC7300 io.groups reflector a PDF documenting a modification to do with instabilities found with the IC7300 power amplifier when the Kuhne board was disengaged and carried out the modifications which made no difference to my problems which in all honestly wasn't surprising.

I've now decided to remove the modification and go back to the combiner and attenuator method of driving the transverter which was far more stable and had no issues.

Another observation is the fact I kept seeing some IM products in the adjacent 3kHz from where I was operating from which I just couldn't get rid of it wasn't bad about -25dB in relation to output and wasn't always present but with the modification removed it vanished completely to the point where any IM product is now at least -35db at worst.

Iceni 70cm Transverter from G4DDK - Part 4

I finally got around to finishing the Iceni transverter as depicted below.

Finished Iceni Transverter

The unit is configured to give 17dBm for 0dBm of drive which is then reduced a bit more so that the mini-kits.com.au 70cm PA gives 30dBm which is great for the BNOS 432-1-50 PA I have.

All in all a great project which I'm extremely happy with.

Iceni 70cm Transverter from G4DDK - Part 3

I've finally started on finishing the Iceni transverter I've used the same case layout as the Anglian.

Front Panel

PA Heatsink

Rear Panel

Internal Layout

I've a bit more room inside the Iceni as I've used a Tohtsu CX-120A relay in place of the old Pye relay I had available for the Anglian which is a pity as the Pye was a nicer relay and had better isolation in comparison.  

Next up on the list is to start wiring it all up but least the hard bit is now done as I hate enclosure fabrication. 

I fitted a Kuhne QH30A heater to the Iceni' crystal so it'll need to be realigned but I'll wait until I've made up the LO inject cable and socket as the extra capacitance knock the frequency off by about a 100Hz.

Anglian 3L 2m Transverter from G4DDK - Part 3

Finally ready to try driving the Anglian from the rig I needed to connect it up.   Originally I was going to use the Kuhne transverter interface for the IC7300 but after some consideration decided to actually use a combiner along with a 20dB 30W attenuator though there is obviously a loss incurred in the RX path switching between the Anglian and Iceni will however be easier.

I bought the attenuator from eBay from for the bargain price of £25 these things are now cheap as chips from China and when I tested the unit with a VNA gave 20dB of attenuation at 50ohms from 1MHz to 600MHz which is as far as I bothered but the device will apparently work up to 3GHz but I couldn't vouch for that.

The combiner is a Merrimac 2 way 0 deg inductive unit from rf-microwave.com which cost just over £40 pounds which is cheaper than the mini-circuits equivalent unit and more than up to the job.

Merrimac combiner with 20dB 30W attenuator

With my Yaesu FT991 set to give 40dBm of drive which  will provide 20dBm to the Anglian once passed through the attenuator I measured and output as 39dBm so some additional attenuation is required between the Anglian and the PA.

With an extra 16dB of attenuation placed between the Anglian and the PA I measured just under 37dBm out which is good enough to drive my little Microset SR100 amplifier.   

I couldn't measure the 2nd and 3rd harmonic product with my equipment but I did a quick check with my SDR and I couldn't see anything on the SDR# waterfall.

Anglian 3L 2m Transverter from G4DDK - Part 2

Well blow me I went to align the TX chain on the Anglian and low and behold no output, this turned out to be IC7 being grounded once this was resolved the TX chain worked as expected giving out 20dBm for 0dBm of drive.

I've had all manner of issues with this Anglian 99% caused by the builder.   I've come to the conclusion that solder paste though easy to use can cause issues if a little too much is used.   I never had this issue with the Iceni however did spend more time cleaning the board and that seems to have paid dividends with the Iceni, so mental note to self don't skimp on making sure any solder paste residue is removed.

I also had a replacement QH40A heater from Kuhne arrive which I duly fitted and low and behold the exact same issue in that as the heater heats up the frequency slowly drifts up to the correct frequency and then suddenly drop by around 500Hz and then slow drifts back up again before repeating.   I may ask Sam if he has another crystal I could buy just to experiment with however as I have a GPSDO there is no real need, even without the heater after a 10 minute warm up period the unit only drifts by a few cycles.

Sam also does an 8W Class AB amplifier which has good linearity when limited to 5W PEP for the Anglian which is simple to build.  The unit draws around 1.5A with a supply voltage of 12.8V.

Sadly I omitted to take any photographs of the PA but you can almost see the unit in the pictures of the completed transverter below.

The last thing to do is plug it all in and test the output from the PA doesn't exceed 5W PEP.

Front Panel

Rear Panel

The inside.

Anglian 3L 2m Transverter from G4DDK - Part 1

With the success of building the Iceni transverter from G4DDK I decided I'd also purchase and build Sam's Anglian 3L 2m transverter as well which I'd heard glowing reviews for.

The Anglian 3L is of a similar design as the Iceni using much of the same circuitry and form factor.

Here's a list of specifications from Sam's website.

Parameter	Performance
RX noise figure	1.6-1.8dB
RX gain	25-26dB
RX IIP3	Better than 0dBm
TX gain	20dB (35dB with optional TX IF stage)
28MHz Drive required for +20dBm 144MHz output	0dBm (-15dBm with IF amplifier)
Power output (Saturated/P1dB)	+22/+20dBm
Harmonic output (2nd/3rd/higher) at saturation/td>	-40dBc/-50dBc/<-60dBc
Image frequency output suppression	<70dBc
LO suppression	<70dBc
Transmit sideband noise	Better than -140dBc/Hz at 20kHz offset

The kit went together fairly easily but you must double check both the parts list and circuit diagram as well as the assembly documents to get it right.

The Anglian 3L uses the same PCB as the original Anglian 3 with either some components changed, added or even removed so you can't just follow the silkscreen print on the board.

I found a few omissions and errors with the documents but Sam is always willing to aid assistance and be told of mistakes so he can fix them and in fact has a searchable PDF if you ask him.

The completed module can be seen below, sadly I omitted to take any photographs during the build.

Anglian 3L after much fault finding.

On first power up I found there was nearly 750mA of current draw instead on the 250mA the build document said there would be.  I removed both TR4 and TR5 from the unit so that both the receive and transmit chains would be isolated from the rest of the circuit and plugged the unit back in and measured a current draw of 70mA with a 12V supply which is in agreement with what Sam said the unit would draw.

Next I replaced TR4 and again measured the current draw which has now returned to the 750mA I originally measured which indicated the error was in the receive chain so I removed TR4 again and then replaced TR5 and measured the current draw again which was now 80mA proving the error was in fact in the receive chain, I then refitted TR4 again.

Knowing the problem was in the receive chain I slowly isolated each part of the circuit until I ended up with only the PSA4-5043 MMIC IC3 left in the circuit, sadly removing it without a reflow hot air gun is a pain in the backside and in fact I ended up destroying it so it was back to Sam to ask for a replacement which he kindly sent out.   I couldn't see any shorted tracks under the microscope and I can only assume that I had a short on the underneath of the IC3 which I couldn't see, anyway with the replacement fitted the unit now had a current draw of 260mA hooray!

With the unit now seeming to be working the next thing to do was to set the oscillator to 116MHz with an output of around 20dBm, well blow me there was no output from the oscillator a quick check with the voltmeter showed there was no voltage on the collector of TR2.  After a bit of head scratching I realised R13 was missing from the board,  the silkscreen was marked L8 and not R13 so it got omitted during the initial construction, I said double check the circuit against the silkscreen as there is a few of these changes that are easy to miss if you're not careful.

I could not get the oscillator on frequency it was also over 200Hz off and had a very sharp adjustment so I ended up removing L27 to give a little leeway in the adjustment and managed to get the oscillator bang on frequency.

On a side note I had a Kuhne QH40A heater attached to the crystal.  The heater keeps a constant temperature of 40C, though the crystal is cut for a temperature inflexion point of 25C, now this worked great with the Iceni but caused horrendous drift on the Anglian and the only reason I can think of the heater was actually heating above 40C so I've removed it for the time being.

Sam recommends the QH40A with both the Iceni and Anglian and it worked really well with the Iceni but if you suffer frequency drift with the QH40A fitted don't assume it's the Anglian drifting but irregularities with the heater instead.  I did have a word with Kuhne regards reducing the voltage the heater to see if that would lower the temperature but they say it won't make a difference so I need to order another.

Next thing to do is align the receiver this involves adjusting L14, 15, 16 and 20 using the coilcraft trimming tool included with the kit.   Now the build document said to set a receiver to 29MHz and connect the Anglian then try and equalise the noise across 28 - 30 MHz by adjust the L14 - 16.   I found to my horror that I appeared to have no receive output from the receiver, bangs head on wall, bother!

To workout where the fault  I injected a 144MHz signal into the Anglian's RF_RX port and with an oscilloscope 1x probe connected an RTL2823U dongle and SDR# set to 144MHz traced the signal through to the mixer I then switched the SDR# frequency to 29MHz and traced though to the LPF where I discovered yet another short this time on C24 I removed and refitted it which resolved the problem.

Even though the receive chain was now fully operational I still couldn't hear an difference in noise level when adjusting the inductors and in the end came to the conclusion that either my hearing is a little dodgy, the fact I couldn't turn the AGC off on the Yaesu FT991 receiver I have or even both.

To get over this problem I again connected a signal generator to the RF_RX port injected a 144MHz into the Anglian I then adjusted the coils for maximum signal which I then repeated at 143 and 145MHz until I had a equalised the read signals across the band.   The assembly document said the inductors would probably be a few turns below the top of the can but you can see in the picture below mine didn't end up like that at all.

The three inductors in line are for the RX alignment.

I maybe able to redo the alignment once I have the Icom 7300 out of the box but until then I'll leave the adjustment as is.

Just to be certain everything up to this point appeared to be working I connected an antenna to the Anglian and tuned in the GB3VHF beacon on 144.4285MHz and ran WSJT up to make sure the continuous tone the beacon transmits between the JT65B and Morse sequences fell on the 1.5kHz mark on water fall and I was pleasantly surprised to see it was with a few cycles of where it should have been, though bear in mind I did use a GPSDO due there being no heater currently fitted so it should have been pretty much spot on.

The next thing to do is to the align the transmit chain and write part two. ;-)

Kuhne Electronics IC7300 IF Transverter Mod Board

While building the Iceni 70cm transverter I thought of combining the separate TX and RX IF's with either a simple resistive Wilkinson combiner or using a lumped component Wilkinson.

But the guys at Kuhne Electronics however do a simple mod board consisting of a couple of relays and diodes and a single resistor which will give separate TX and RX IF outputs so I bought the mod board to try it out.  The beauty of this method is there will be no attenuation loss in the RX path.

The supplied PCB looks to be good quality though the connectors are RCA phono sockets and it would have been nice to have BNC's instead, the only other thing that would have been nice is an adjustable attenuator on the IF out as according the Kuhne the IF output will be about 25dBm and Sam's transverters require 0dBm.

The board itself took 10 minutes to construct having so few components.   I've yet to fit it but that just involves making a couple of coax tails made out of 35ohm 3.6mm rigid coax which plugs into the IC7300 RF unit and then soldered to the Kuhne IF board once the right length has been determined.

The board sits between the RF PCB and PA PCB.  When the mod board is activated it provides a 50ohm load on the PA input while passing the feeds from the RF PCB out to the transverter.

The board operates by supplying 12V to switch the relays.   I'll update the blog once I tried the board out.

Kuhne Electronic IC7300 IF break out board.

Iceni 70cm Transverter from G4DDK - Part 2

I've finally finished the G4DDK Iceni 70cm transverter module.

The unit seemed checkout the initial tests as specified in the build document however when I attached the module to my spectrum analyser I had no output from the oscillator.   I checked the voltages on the the couple of transistors in the oscillator circuit all of which seemed to be correct the ball park I emailed Sam for suggestions.

Sam suggested making sure all the components were correctly soldered to the ground plane which to my eyesight seemed they were so Sam kindly offered to take a look at the unit for me.

Sam very kindly not only fixed the couple of bad solder joints I had on the unit, which he suggested was down to the iron not being hot enough and so not conducting enough heat into the ground plane, he also aligned the unit for me.  Strangely he found one inductor which was open circuit and I have no idea as to how that could have happened.

He also commented on how well the unit was constructed which was a nice vote of confidence in my ability with SMD components being only the second project undertaken with these minute components the MMIC's are particularly tricky as detailed in the last post on the Iceni.

To say I'm impressed with Sam's product and assistance is an under statement to the point I've just ordered the Anglian 3L and 8W short PA from him as well.

So with the Iceni built and up and running I fitted a Kuhne QH40A crystal heater for added stability.

The total amount of man hours to complete the unit was around nine hours from start to finished including the fabrication of the housing.

I've now ordered a 7W PA from mini-kits in Australia, so once that has arrived and is constructed I get on with sorting out the power supply and a nice box for it all.

The finished Iceni transverter

Iceni 70cm Transverter from G4DDK - Part 1

I have plunged myself into the world of transverters by buying the 70cm Iceni from Sam Jewell G4DDK.

Here's a list of specifications from Sam's website.

Parameter	Measured	Comments
RX noise figure	2.0dB	Usual uncertainties apply
RX gain	21dB +/-1dB	Fixed Gain
RX maximum input	0dBm	Max non-damage level
RX IIP3	-10dBm +/-1dB	Measured at -37dBm/tone
RX bandwidth	8.5MHz	3dB bandwidth
TX gain	16.5dB +/-0.5dB	Tx attenuator at minimum
TX IF input level	0dBm	Max +6dBm at attenuator minimum
TX output power	+20dBm	At +6dBm IF input. 0dBm max IF input recommended
TX IMD	-50dBc/-38dBc	+7dBm/+10dBm per tone at output
TX spurious	<-60dbc	Except second harmonic -53dBc at +16.5dBm output

The kit doesn't on the face of it look too complicated, but care must be taken when assembling.   All the problems I encountered were all RTFM issues.

Sam suggested to mark and drill the tin enclosure first which went quite well until I had scribed the first few line on the box only to realise what I considered to be the top of the PCB was in fact the bottom, again an RTFM problem on my part.  Make sure you have sharp drill bits tin isn't the easiest material to drill though.  It took about 45 minutes to mark up and 10 minutes to drill.

Tin box marked and drilled.

To assemble the PCB you do need a good pair of tweezers, a decent eye glass and a fine tipped iron.  Sam  recommended using 0.8mm tin/lead mix solder but I went for solder paste instead, dabbing the correct amount on the pads using a cocktail stick, which was recommended to me by a friend.  The jury is still out on which way is best when the solder paste flowed correctly it was much easier and gave a good looking joint but you do need to keep the board clean and not apply to much paste.

I washed the board after fitting the resistors by soaking in a bath of isopropyl for an hour then agitating with a toothbrush to remove any small solder balls and left over paste.  Once the wash has been completed go over the joints with the eye glass checking that the paste hasn't just blobbed up onto the end the component and has in fact made a good joint.   I washed the board after fitting each set of components but omitted devices like the variable capacitors, electrolytic caps, variable inductors and the ADE-13 mixer all of which wouldn't take kindly to the ingress of solder paste.

If I was going to build another one I'd actually fit the ceramic caps first as most are coupling caps and so could easily be tested for shorts which wasn't the case once I had fitted the resistors.

The only device I had real trouble with was fitting the PSA4-5043 MMIC amps they're damn fiddlely to fit.  Now that I tried fitting them I'd have done it differently by fitting the main ground leg by using the 0.8mm solder to apply a blob on the ground pad and then using the tweezers slide the device into place while keeping the solder blob molten.    I found when using the paste as I couldn't see the solder pads getting the orientation wrong was all too easy.   I'm now awaiting for two replacements from Sam as I ended up damaging two of the devices trying to remove them due to the orientation issue.

You can see in the picture below how small the MMIC amps, circled in red, really are.  The markings on the green background are 1cm squares.

The Iceni with an MMIC encircled in red 

I had a couple of parts go awol in the construction which Sam has very kindly replaced gratis he did however charge me for the additional two MMIC's at three pounds each plus postage which is very fair.

Once the new parts arrive I'll need to fit the parts and then finally the MX1 and inductors I can then move onto the fitting the PCB into the tin box.

Part two coming soon.